Who or what is responsible for initializing wiimote extensions (such a nunchuk) and changing the wiimote's Data Reporting mode after the initial setup dolphin does that includes just the base buttons? Is it dolphin, the game, something else?

I've added logging to Wiimote::IOWrite and Wiimote::IORead to hopefully see all traffic between dolphin and my wiimote clone, and all I see when I start a game such as Mario Kart is,

Code:

IOWrite: a1 15 00
IOWrite: a2 17 00 00 17 70 00 01

Apart from the

Code:

IORead: a1 30 XX XX

that are caused by me pressing buttons.

"a1 15 00" is sent by dolphin itself, while the "a2 17..." appears be triggered by the emulation.
But I never see any response for these. What's supposed to happen? I can't figure out what
sort of command "a2 17 ..." is either.